This is a data analysis grant to quantify rhythms in social interaction and physiological activity during mother-infant interaction in term and preterm neonates, and to relate interaction rhythms to rhythms in cardiac and respiratory activity. Methods of spectral analysis will be used to study rhythmic activity in 24 term and 24 preterm infant-mother dyads who were videotaped during a 3-minute face-to-face interaction when these infants were term, and 2 and 4 weeks later. During the 3-minute session, dyadic interaction was coded and cardiac and respiratory activity computer integrated with the video image of the infant and mother. This study will contribute to our understanding of the genesis and biological basis of social interaction and early human communication. The mental health relevance of this work lies in this understanding of normal developmental processes, in differences between term and preterm infants that may be at the basis of disordered interactions, and in differences in neurophysiological functioning that may affect development in preterm infants.